This is a multidisciplinary study of problems related to the etiology, pathogenesis and therapy of neoplastic disorders in children. The emphasis is on the study of acute leukemia. Human material obtained from patients on the Hematology and Oncology Service at Texas Children's Hospital, which serves as a referral center for this geographical area, is used in a coordinated manner to provide a constant source of clinical specimens including important control materials. The project was started in 1961 and gradually expanded to include: study of the epidemiology of acute leukemia by family groups and by analysis of case distribution in Harris County, Texas; study of leukemic cell lines for virus particles by electron microscopy; study of the effects of the inoculation of newborn baboons with material obtained from children with acute leukemia; study of the behavior and treatment of infection in children with acute leukemia; study of the possible common etiology or relationship between acute leukemia and infectious mononucleosis in children; study of the leukocyte types by use of monospecific tissue typing antisera to determine high incidence leukemia family patterns and the reactivity of leukemic cells to antilymphocytic globulin.